U.S. patent number 8,576,351 [Application Number 12/705,076] was granted by the patent office on 2013-11-05 for illuminating lens, lighting device, surface light source, and liquid-crystal display apparatus.
This patent grant is currently assigned to Panasonic Corporation. The grantee listed for this patent is Tomoko Iiyama, Syunsuke Kimura, Daizaburo Matsuki. Invention is credited to Tomoko Iiyama, Syunsuke Kimura, Daizaburo Matsuki.
United States Patent |
8,576,351 |
Kimura , et al. |
November 5, 2013 |
Illuminating lens, lighting device, surface light source, and
liquid-crystal display apparatus
Abstract
An illuminating lens includes a main body and a ring portion.
The main body has a light exit surface, and the light exit surface
has a first light exit surface recessed toward a point on the
optical axis and a second light exit surface extending outwardly
from the periphery of the first light exit surface. The first light
exit surface has a transmissive region in the center thereof, and a
total reflection region on the peripheral side thereof. The ring
portion has a back surface configured to guide the light that has
been emitted from a light source, totally reflected repeatedly at
the light exit surface, and then entered the ring portion to an end
surface by total reflection.
Inventors: |
Kimura; Syunsuke (Hyogo,
JP), Matsuki; Daizaburo (Osaka, JP),
Iiyama; Tomoko (Osaka, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Kimura; Syunsuke
Matsuki; Daizaburo
Iiyama; Tomoko |
Hyogo
Osaka
Osaka |
N/A
N/A
N/A |
JP
JP
JP |
|
|
Assignee: |
Panasonic Corporation (Osaka,
JP)
|
Family
ID: |
42559598 |
Appl.
No.: |
12/705,076 |
Filed: |
February 12, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100208167 A1 |
Aug 19, 2010 |
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Foreign Application Priority Data
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Feb 12, 2009 [JP] |
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2009-029350 |
Jun 19, 2009 [JP] |
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2009-146770 |
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Current U.S.
Class: |
349/62; 362/327;
362/311.06; 362/311.02; 349/69; 362/329; 362/328; 362/333; 349/64;
362/334; 362/335 |
Current CPC
Class: |
G02B
19/0028 (20130101); G02F 1/133606 (20130101); G02B
19/0061 (20130101); G02F 1/133611 (20130101); G02F
1/133605 (20130101); G02F 1/133607 (20210101); G02F
1/133603 (20130101) |
Current International
Class: |
G02F
1/1335 (20060101); F21V 5/00 (20060101); F21V
3/00 (20060101); F21V 5/04 (20060101) |
Field of
Search: |
;349/62,64,69
;362/311.02,311.06,327-329,333-336 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2004-087411 |
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Mar 2004 |
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JP |
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2005-011704 |
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Jan 2005 |
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JP |
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2005-317977 |
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Nov 2005 |
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JP |
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2006-005791 |
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Jan 2006 |
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JP |
|
2006-113556 |
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Apr 2006 |
|
JP |
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2006-147448 |
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Jun 2006 |
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JP |
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2006-252841 |
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Sep 2006 |
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JP |
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2006-309242 |
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Nov 2006 |
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JP |
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3875247 |
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Nov 2006 |
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JP |
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2007-026702 |
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Feb 2007 |
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JP |
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2007-034307 |
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Feb 2007 |
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JP |
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2007-048775 |
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Feb 2007 |
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JP |
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2007-096318 |
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Apr 2007 |
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JP |
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2007-102139 |
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Apr 2007 |
|
JP |
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2007-287479 |
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Nov 2007 |
|
JP |
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2008-015288 |
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Jan 2008 |
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JP |
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2008-305923 |
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Dec 2008 |
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JP |
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10-2006-0040502 |
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May 2006 |
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KR |
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2007/021149 |
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Feb 2007 |
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WO |
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Other References
Co-pending U.S. Appl. No. 12/704,813, filed Feb. 12, 2010. cited by
applicant .
Co-pending U.S. Appl. No. 12/705,016, filed Feb. 12, 2010. cited by
applicant .
Co-pending U.S. Appl. No. 12/704,926, filed Feb. 12, 2010. cited by
applicant .
Co-pending U.S. Appl. No. 12/720,249, filed Mar. 9, 2010. cited by
applicant.
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Primary Examiner: Merlin; Jessica M
Attorney, Agent or Firm: Hamre, Schumann, Mueller &
Larson, P.C.
Claims
What is claimed is:
1. An illuminating lens for spreading light emitted from a light
source so that a surface to be irradiated is irradiated with the
spread light, the lens comprising: a main body to be disposed over
the light source; and a ring portion joined to a periphery of the
main body so as to be located around the light source, wherein the
main body includes: a light entrance surface through which the
light emitted from the light source enters the lens; and a light
exit surface through which the light that has entered the lens
exits the lens, the light exit surface has a first light exit
surface and a second light exit surface, the first light exit
surface being recessed toward a point on an optical axis of the
illuminating lens, and the second light exit surface extending
outwardly from a periphery of the first light exit surface to form
a convex surface, the first light exit surface has a transmissive
region located in the center of the first light exit surface and a
total reflection region located around the transmissive region, the
transmissive region being capable of transmitting light that has
been emitted from a starting point at a relatively small angle with
respect to the optical axis and then reached the first light exit
surface, when a position of the light source on the optical axis is
defined as the starting point, and the total reflection region
being capable of totally reflecting light that has been emitted
from the starting point at a relatively large angle with respect to
the optical axis and then reached the first light exit surface, the
second light exit surface has a shape capable of transmitting
approximately the entire amount of light that has been emitted from
the starting point and then directly reached the second light exit
surface, and of totally reflecting approximately the entire amount
of the light that has been totally reflected at the total
reflection region and then reached the second light exit surface,
the ring portion has a front surface extending outwardly from a
periphery of the light exit surface, a back surface extending
outwardly from a periphery of the light entrance surface, and an
end surface connecting an outer edge of the front surface and an
outer edge of the back surface, the back surface has a shape such
that light that has been emitted from the light source, totally
reflected repeatedly at the light exit surface, and then entered
the ring portion is guided to the end surface by total reflection,
and the end surface has a shape such that light that has been
totally reflected at the back surface and reached the end surface
is refracted to reach the surface to be irradiated.
2. The illuminating lens according to claim 1, wherein the light
exit surface is axisymmetric with respect to the optical axis.
3. The illuminating lens according to claim 1, wherein the back
surface has a first region extending outwardly from the periphery
of the light entrance surface to form a convex surface and a flat
second region extending continuously from the first region.
4. The illuminating lens according to claim 3, wherein the second
region has a larger width than the first region in a direction
radially outward from the optical axis.
5. The illuminating lens according to claim 3, wherein a distance
from the light entrance surface to the second region is longer than
a maximum distance from the light entrance surface to the light
exit surface in an optical axis direction in which the optical axis
extends.
6. The illuminating lens according to claim 3, wherein a tangential
direction of an outermost periphery of the second light exit
surface is approximately parallel to that of an innermost periphery
of the first region in a cross-sectional view including the optical
axis.
7. The illuminating lens according to claim 3, wherein a tangential
direction of an innermost periphery of the first region is parallel
to the optical axis in a cross-sectional view including the optical
axis.
8. The illuminating lens according to claim 1, wherein the entire
second light exit surface transmits the light that has been emitted
from the starting point.
9. The illuminating lens according to claim 1, wherein the second
light exit surface totally reflects a part of the light that has
been emitted from the starting point and then directly reached the
second light exit surface, and transmits the remaining part of the
light.
10. A lighting device comprising: a light emitting diode for
emitting light; and an illuminating lens for spreading light
emitted from the light emitting diode so that a surface to be
irradiated is irradiated with the spread light, wherein the
illuminating lens is the illuminating lens according to claim
1.
11. A surface light source comprising: a plurality of lighting
devices arranged in a plane; and a diffusing plate disposed to
cover the plurality of lighting devices, the diffusing plate being
configured to receive on one surface thereof light emitted from the
plurality of lighting devices and to emit the light from the other
surface thereof in a diffused manner, wherein each of the plurality
of lighting devices is the lighting device according to claim
10.
12. The surface light source according to claim 11, further
comprising: a substrate on which the light emitting diode included
in each of the plurality of lighting devices is mounted, the
substrate facing the diffusing plate with the plurality of lighting
devices being disposed therebetween; and a reflecting plate
disposed on the substrate to cover the substrate with the light
emitting diodes being exposed.
13. A liquid-crystal display apparatus comprising: a liquid-crystal
panel; and the surface light source according to claim 11 disposed
behind the liquid-crystal panel.
14. The illuminating lens according to claim 1, wherein: the light
entrance surface having a recess formed toward the light exit
surface at the optical axis of the illuminating lens; and the light
source is configured to be disposed into the recess of the light
entrance surface.
15. The lighting device according to claim 10, wherein an air space
is provided between the light emitting diode and the light entrance
surface such that the light emitting diode does not directly
contact the light entrance surface.
16. The illuminating lens according to claim 1, wherein the second
light exit surface faces toward the surface to be irradiated.
17. The illuminating lens according to claim 1, wherein a portion
of the second light exit surface faces toward the surface to be
irradiated.
18. The illuminating lens according to claim 1, wherein: at least a
portion of the second light exit surface is disposed between the
light entrance surface and the surface to be irradiated, and is
disposed opposite to the light entrance surface.
19. The illuminating lens according to claim 1, wherein: the first
light exit surface has a discontinuity between the first light exit
surface and the second light exit surface.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illuminating lens for widening
a range of transmission directions for light from a light source
such as a light emitting diode, and to a lighting device using this
illuminating lens. The present invention further relates to a
surface light source including a plurality of lighting devices, and
to a liquid-crystal display apparatus in which this surface light
source is disposed behind a liquid-crystal panel to serve as a
backlight.
2. Description of Related Art
In a conventional backlight of a large-sized liquid-crystal display
apparatus, a number of cold cathode tubes are disposed immediately
below a liquid-crystal panel, and these cold cathode tubes are used
with other members such as a diffusing plate and a reflecting
plate. In recent years, light emitting diodes have been used as
light sources for backlights. Light emitting diodes have increased
their efficiency recently, and are expected to serve as low-power
light sources to replace fluorescent lamps. In the case where light
emitting diodes are used as a light source in a liquid-crystal
display apparatus, the power consumption of the apparatus can be
reduced by controlling the light and dark states of the light
emitting diodes according to an image to be displayed.
In a backlight of a liquid-crystal display apparatus using light
emitting diodes as a light source, a large number of light emitting
diodes are disposed therein instead of cold cathode tubes. The use
of a large number of light emitting diodes allows the entire
surface of the backlight to have uniform brightness, but the need
for such a large number of light emitting diodes is an obstacle to
cost reduction. In view of this, attempts to increase the output
power of each light emitting diode to reduce the required number of
light emitting diodes have been made. For example, Japanese Patent
No. 3875247 has proposed a lens that is designed to provide a
uniform surface light source with a reduced number of light
emitting diodes.
In order to obtain a uniform surface light source with a reduced
number of light emitting diodes, the area to be irradiated with the
light emitted from each light emitting diode needs to be increased.
That is, light emitted from each light emitting diode needs to be
spread to obtain a wider range of transmission directions for light
from the diode. For this purpose, in Japanese Patent No. 3875247, a
lens having a circular shape in a plan view is disposed on a light
emitting diode as a chip to control the directivity of the chip.
The light exit surface of this lens, through which light exits the
lens, has a shape such that a portion in the vicinity of the
optical axis is a concave and a portion surrounding the concave is
a convex extending continuously from the concave.
On the other hand, JP 2008-305923 A has proposed a lens that is
designed to provide a more uniform surface light source. In this
lens, light that has been Fresnel reflected at the light exit
surface of the lens back to the light entrance surface side thereof
is reflected again by total reflection to be guided toward the
surface to be irradiated.
A light emitting diode as a chip emits light mostly in the front
direction of the light emitting diode chip. In the lens disclosed
in Japanese Patent No. 3875247, light that has been emitted in the
front direction of the chip is refracted at the concave surface in
the vicinity of the optical axis and diffused. As a result, the
surface to be irradiated is illuminated to have a wide illuminance
distribution with a reduced illuminance in the vicinity of the
optical axis.
In the lens disclosed in Japanese Patent No. 3875247, however, the
light emitted from the light source needs to be refracted, and
therefore the difference in height between the concave and the
convex must be reduced to a certain level. That is, there is a
limit to a widening of the range of transmission directions for
light from the light source. The lens disclosed in JP 2008-305923 A
has the same limit because it is designed to distribute the light
emitted from the chip by utilizing the refraction of the light.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an illuminating
lens capable of further widening the range of transmission
directions for light from a light source, and to provide a lighting
device, a surface light source, and a liquid-crystal display
apparatus each including this illuminating lens.
In order to achieve the above object, the present inventors have
considered it important, in obtaining a wider range of transmission
directions for light from a light source, to distribute radially
the intense light that has been emitted in the front direction of
the light emitting diode chip, and come up with an idea of
distributing radially the light emitted in the front direction of
the light emitting diode chip by utilizing intentionally the total
reflection of the light. Accordingly, the present inventors have
conceived an illuminating lens described below.
That is, the illuminating lens is a lens for spreading light
emitted from a light source so that a surface to be irradiated is
irradiated with the spread light, and includes: a light entrance
surface through which the light emitted from the light source
enters the lens; and a light exit surface through which the light
that has entered the lens exits the lens. The light exit surface
has a first light exit surface and a second light exit surface. The
first light exit surface is recessed toward a point on an optical
axis of the illuminating lens, and the second light exit surface
extends outwardly from a periphery of the first light exit surface
to form a convex. The first light exit surface has a transmissive
region located in the center of the first light exit surface and a
total reflection region located around the transmissive region.
When the position of the light source on the optical axis is
defined as a starting point, the transmissive region transmits
light that has been emitted from the starting point at a relatively
small angle with respect to the optical axis and then reached the
first light exit surface, and the total reflection region totally
reflects light that has been emitted from the starting point at a
relatively large angle with respect to the optical axis and then
reached the first light exit surface. The second light exit surface
has a shape capable of transmitting approximately the entire amount
of light that has been emitted from the starting point and then
reached the second light exit surface.
In the illuminating lens configured as described above, the range
of transmission directions for light from the light source can be
widened more by utilizing positively the total reflection of light.
As shown in FIG. 21, in this illuminating lens, the light is
totally reflected at the total reflection region of the first light
exit surface in the light exit surface 112. Then, a part of the
light again is totally reflected repeatedly at the second light
exit surface extending outwardly from the first light exit surface,
and returns to the light entrance surface 111 side. The light that
has returned to the light entrance surface 111 side passes through
the light entrance surface 111, and then is reflected at the member
130 (for example, a substrate) that faces the light entrance
surface 111 so as to be guided toward the surface to be irradiated.
In this case, the light that has been reflected at the member 130
to be guided to the surface to be irradiated travels in the
direction away from the optical axis or travels in the direction
toward the optical axis, as shown in FIG. 21. In order to obtain a
wider illuminance distribution on the surface to be irradiated, it
is effective also to guide the light that has returned to the light
entrance surface 111 side in the direction away from the optical
axis. The present invention has been made in view of the above
circumstances.
The present invention provides an illuminating lens for spreading
light emitted from a light source so that a surface to be
irradiated is irradiated with the spread light. The lens includes:
a main body to be disposed over the light source; and a ring
portion joined to a periphery of the main body so as to be located
around the light source. In this illuminating lens, the main body
includes: a light entrance surface through which the light emitted
from the light source enters the lens; and a light exit surface
through which the light that has entered the lens exits the lens.
The light exit surface has a first light exit surface and a second
light exit surface. The first light exit surface is recessed toward
a point on an optical axis of the illuminating lens, and the second
light exit surface extends outwardly from a periphery of the first
light exit surface to form a convex. The first light exit surface
has a transmissive region located in the center of the first light
exit surface and a total reflection region located around the
transmissive region. The transmissive region transmits light that
has been emitted from a starting point at a relatively small angle
with respect to the optical axis and then reached the first light
exit surface, when a position of the light source on the optical
axis is defined as the starting point. The total reflection region
totally reflects light that has been emitted from the starting
point at a relatively large angle with respect to the optical axis
and then reached the first light exit surface. The second light
exit surface has a shape capable of transmitting approximately the
entire amount of light that has been emitted from the starting
point and then reached the second light exit surface, and of
totally reflecting approximately the entire amount of the light
that has been totally reflected at the total reflection region and
then reached the second light exit surface. The ring portion has a
front surface extending outwardly from a periphery of the light
exit surface, a back surface extending outwardly from a periphery
of the light entrance surface, and an end surface connecting an
outer edge of the front surface and an outer edge of the back
surface. The back surface has a shape such that light that has been
emitted from the light source, totally reflected repeatedly at the
light exit surface, and then entered the ring portion is guided to
the end surface by total reflection. The end surface has a shape
such that light that has been totally reflected at the back surface
and reached the end surface is refracted to reach the surface to be
irradiated.
Herein, "approximately the entire amount" means at least 90% of the
entire amount. It may be the entire amount, and may be an amount
slightly smaller than the entire amount.
The present invention also provides a lighting device including: a
light emitting diode for emitting light; and an illuminating lens
for spreading light emitted from the light emitting diode so that a
surface to be irradiated is irradiated with the spread light. This
illuminating lens is the above-mentioned illuminating lens.
The present invention further provides a surface light source
including: a plurality of lighting devices arranged in a plane; and
a diffusing plate disposed to cover the plurality of lighting
devices, and configured to receive on one surface thereof light
emitted from the plurality of lighting devices and to emit the
light from the other surface thereof in a diffused manner. Each of
the plurality of lighting devices is the above-mentioned lighting
device.
The present invention still further provides a liquid-crystal
display apparatus including: a liquid-crystal panel; and the
above-mentioned surface light source disposed behind the
liquid-crystal panel.
According to the present invention, it is possible to obtain a
wider range of transmission directions for light from the light
source. Furthermore, according to the present invention, the ring
portion allows the light that has returned to the light entrance
surface side to be guided in the direction away from the optical
axis, and thus a wider illuminance distribution on the surface to
be irradiated can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an illuminating lens according to
a first embodiment of the present invention.
FIG. 2 is an enlarged view of the main portions of FIG. 1.
FIG. 3 is a diagram showing optical paths of light rays that reach
a first light exit surface of a main body in the illuminating lens
according to the first embodiment of the present invention.
FIG. 4 is a diagram showing optical paths of light rays that reach
a second light exit surface directly from a light entrance surface
of the main body in the illuminating lens according to the first
embodiment of the present invention.
FIG. 5 is a diagram showing optical paths of light rays that are
totally reflected at a total reflection region of the first light
exit surface and then reach the second light exit surface of the
main body in the illuminating lens according to the first
embodiment of the present invention.
FIG. 6 is a diagram showing optical paths of light rays that are
totally reflected at the second light exit surface and then reach a
first region of a back surface of the ring portion in the
illuminating lens according to the first embodiment of the present
invention.
FIG. 7 is a diagram showing an optical path of a light ray that is
totally reflected at the first region and then reaches a second
region of the back surface of the ring portion in the illuminating
lens according to the first embodiment of the present
invention.
FIG. 8 is a diagram showing optical paths of light rays that are
totally reflected at the first region and the second region of the
back surface and then reach an end surface of the ring portion in
the illuminating lens according to the first embodiment of the
present invention.
FIG. 9 is a schematic diagram of a lighting device according to a
second embodiment of the present invention.
FIG. 10 shows an illuminance distribution obtained by using the
lighting device according to the second embodiment of the present
invention.
FIG. 11 is a schematic diagram showing an example in which a
reflecting plate is disposed behind the lighting device according
to the second embodiment of the present invention.
FIG. 12 shows an illuminance distribution obtained by using the
lighting device in which the illuminating lens that has been
conceived before is used.
FIG. 13 is a schematic diagram of a lighting device in which an
illuminating lens that has been conceived before is used.
FIG. 14 is a schematic diagram of an example in which a reflecting
plate is disposed behind the lighting device in which the
illuminating lens that has been conceived before is used.
FIG. 15 is a diagram showing dimensions in Example 1 of the
lighting device according to the second embodiment of the present
invention.
FIG. 16 is a graph showing a relationship between .theta.i and
sagY, which represent the shape of the light exit surface in
Example 1 of the lighting device according to the second embodiment
of the present invention (i.e., a graph obtained by plotting the
values in Table 1).
FIG. 17 is a schematic diagram of a surface light source according
to a third embodiment of the present invention.
FIG. 18 is a partial cross-sectional view of the surface light
source according to the third embodiment of the present
invention.
FIG. 19 is a schematic diagram of a liquid-crystal display
apparatus according to a fourth embodiment of the present
invention.
FIG. 20A and FIG. 20B are each a plan view of an illuminating lens
of another embodiment.
FIG. 21 is a schematic diagram of an illuminating lens that has
been conceived before.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
An illuminating lens according to the first embodiment of the
present invention will be described with reference to the
accompanying drawings. FIG. 1 is a schematic diagram of an
illuminating lens 1 according to the first embodiment. The
illuminating lens 1, which is disposed between a light source 20
having directivity and a surface to be irradiated 3, spreads light
emitted from the light source 20 and emits the spread light to the
surface to be irradiated 3. That is, the illuminating lens 1 widens
the range of transmission directions for light from the light
source. In the illuminance distribution on the surface to be
irradiated 3, the illuminance is greatest on the optical axis A
that is the design center line of the illuminating lens 1 and
decreases almost monotonically toward the edge. The light source 20
and the illuminating lens 1 are disposed so that their optical axes
coincide with each other.
Specifically, the illuminating lens 1 includes a main body 1A to be
disposed over the light source 20, and a ring portion 1B joined to
the periphery of the main body 1A so as to be located around the
light source 20.
The main body 1A has a light entrance surface 11 through which the
light emitted from the light source 20 enters the lens and a light
exit surface 12 through which the light that has entered the lens
exits the lens. In the present embodiment, the light exit surface
12 is axisymmetric with respect to the optical axis A. In the
present embodiment, the light entrance surface 11 also is
axisymmetric with respect to the optical axis A. That is, the
central region 11a and the annular region 11b surrounding the
central region 11a of the light entrance surface 11 are in the same
plane. The central region 11a of the light entrance surface 11 is
connected optically to the light source 20. It should be noted that
the light entrance surface 11 need not be axisymmetric with respect
to the optical axis A. For example, the central region 11a may be
recessed in a shape conforming to the shape of the light source 20
(for example, a rectangular shape) so that the light source 20 is
fitted in the recess. The central region 11a need not necessarily
be joined directly to the light source 20. For example, the central
region 11a may be recessed in a hemispherical shape so that an air
space is formed between the central region 11a and the light source
20.
The light emitted from the light source 20 enters the illuminating
lens 1 through the light entrance surface 11, exits the lens 1
through the light exit surface 12, and then reaches the surface to
be irradiated 3. The light emitted from the light source 20 is
spread by the action of the light exit surface 12, and reaches a
large area of the surface to be irradiated 3.
As the light source 20, for example, a light emitting diode can be
used. Light emitting diodes usually are chips with a rectangular
plate shape. Therefore, it is preferable that the light entrance
surface 11 of the illuminating lens 1 have a shape conforming to
the shape of a light emitting diode to fit in close contact with
the light emitting diode. The light emitting diode is in contact
with the light entrance surface 11 of the illuminating lens 1 via a
bonding agent, and connected optically to the light entrance
surface 11. The light emitting diode usually is covered with a
sealing resin to avoid contact with air. As a conventional sealing
resin for a light emitting diode, an epoxy resin, silicone rubber,
or the like is used.
The illuminating lens 1 is made of a transparent material having a
specified refractive index. The refractive index of the transparent
material is, for example, about 1.4 to 1.5. Examples of such a
transparent material include resins such as epoxy resin, silicone
resin, acrylic resin, and polycarbonate, and rubbers such as
silicone rubber. Particularly, it is preferable to use epoxy resin,
silicone rubber, or the like that has been used as a sealing resin
for a light emitting diode.
The light exit surface 12 includes a first light exit surface 121
that is recessed toward a point on the optical axis A, and a second
light exit surface 122 extending radially outwardly from the
periphery of the first light exit surface 121 to form a convex.
Light enters the illuminating lens 1 through the light entrance
surface 11 at a wide range of angles. Light that has entered the
lens at a small angle with respect to the optical axis A reaches
the first light exit surface 121, and light that has entered the
lens at a larger angle with respect to the optical axis A reaches
the second light exit surface 122.
Next, the shapes of the first light exit surface 121 and the second
light exit surface 122 will be described. For that purpose, a
starting point Q (see FIG. 2) is defined first, and then light
emitted from the starting point Q is assumed. As stated herein, the
starting point Q is the position of the light source on the optical
axis A. In the case where a light emitting diode is used as a light
source, the starting point Q is the point of intersection of the
optical axis A and the light emitting surface that is the front
surface of the light emitting diode. That is, the starting point Q
is spaced from the light entrance surface 11 by the thickness of
the above-mentioned bonding agent. When an angle between the
optical axis A and a line connecting the starting point Q and the
boundary between the first light exit surface 121 and the second
light exit surface 122 is .theta.b, light that has been emitted
from the starting point Q at an angle reaches the first light exit
surface 121 or the second light exit surface 122 based on the angle
.theta.b as a threshold angle.
As shown in FIG. 2, the first light exit surface 121 includes a
transmissive region 123 located in the center of the first light
exit surface 121 and a total reflection region 124 located around
the transmissive region 123. The transmissive region 123 transmits
light that has been emitted from the starting point Q at a
relatively small angle of less than a specified value of .theta.p
with respect to the optical axis A and reached the first light exit
surface 121, and the total reflection region 124 totally reflects
light that has been emitted from the starting point Q at a
relatively large angle of .theta.p or more with respect to the
optical axis A and reached the first light exit surface 121. That
is, .theta.p is an angle between the optical axis A and a line
connecting a point P and the starting point Q, when the point P is
a point on the boundary between the transparent region 123 and the
total reflection region 124.
On the other hand, the second light exit surface 122 has a shape
capable of transmitting approximately the entire amount of light
that has been emitted from the starting point Q and reached the
second light exit surface 122, and totally reflecting approximately
the entire amount of the light that has been totally reflected at
the total reflection region 124 and reached the second light exit
surface 122 (see FIG. 4 and FIG. 5). The angle between the optical
axis A and the light emitted from the starting point Q increases
toward the outer edge of the second light exit surface 122. The
angle of the light emitted from the starting point Q with respect
to a normal line at the point on the second light exit surface 122
reached by the emitted light is the incident angle of the light
with respect to the second light exit surface 122. An excessively
large incident angle causes total reflection. The incident angle
needs to be kept small in order to prevent total reflection.
Accordingly, the second light exit surface 122 has a shape such
that the angle between the normal line and the optical axis A
increases with increasing distance from the optical axis A. That
is, the shape of the second light exit surface 122 is a convex.
The entire second light exit surface 122 need not necessarily
transmit the light emitted from the starting point Q (i.e., the
second light exit surface 122 need not transmit the entire amount
of the light). The second light exit surface 122 may have a shape
capable of totally reflecting a part of the light emitted from the
starting point Q and transmitting the remaining part of the
light.
The ring portion 1B is axisymmetric with respect to the optical
axis A in the present embodiment. Specifically, the ring portion 1B
has a front surface 18 extending outwardly from a periphery of the
light exit surface 12, a back surface 16 extending outwardly from a
periphery of the light entrance surface 11, and an end surface 17
connecting an outer edge of the front surface 18 and an outer edge
of the back surface 16.
The back surface 16 has a shape such that light that has been
emitted from the light source 20, totally reflected repeatedly at
the light exit surface 12, and then entered the ring portion 1B is
guided to the end surface 17 by total reflection. On the other
hand, the end surface 17 has a shape such that light that has been
totally reflected at the back surface 16 and reached the end
surface 17 is refracted to reach the surface to be irradiated
3.
For more detail, the back surface 16 has a first region 161
extending outwardly from the periphery of the light entrance
surface 12 to form a convex, and a flat second region 162 extending
continuously from the first region 161. In the present embodiment,
the front surface 18 also is a flat surface parallel to the second
region 162 of the back surface 16 (in other words, perpendicular to
the optical axis A), and the end surface 17 is a cylindrical
surface orthogonal to the second region 162 of the back surface 16
and the front surface 18. The end surface 17 need not necessarily
be parallel to the optical axis A. It may be a tapered shape with
its diameter decreasing from the back surface 16 toward the front
surface 18. The cross-sectional shape of the end surface 17 need
not be linear, and it may be arcuate.
It is preferable that the second region 162 have a larger width
than the first region 161 in the direction radially outward from
the optical axis A. With such a configuration, a larger amount of
light that has been totally reflected at the first region 161 can
be totally reflected at the second region 162, and therefore a
larger amount of light can be guided from the end surface 17 toward
the surface to be irradiated 3.
Furthermore, it is preferable that the distance from the light
entrance surface 11 to the second region 162 is longer than the
maximum distance from the light entrance surface 11 to the light
exit surface 12 in the optical axis direction in which the optical
axis A extends. In other words, it is preferable that the curvature
radius of the first region 161 is as large as possible. With such a
configuration, the amount of light leaking from the lens through
the first region 161 (that is, the amount of light passing through
the first region 161) can be reduced, and therefore the light that
has returned to the light entrance surface 11 side can be utilized
effectively.
Furthermore, it is preferable that a tangential direction of an
outermost periphery of the second light exit surface 122 is
approximately parallel to that of an innermost periphery of the
first region 161 in a cross-sectional view including the optical
axis A. With such a configuration, the amount of light leaking from
the lens through the first region 161 (that is, the amount of light
passing through the first region 161) can be reduced, and therefore
the light that has returned to the light entrance surface 11 side
can be utilized effectively.
It also is preferable that the tangential direction of the
innermost periphery of the first region 161 is parallel to the
optical axis A in a cross-sectional view including the optical axis
A. With such a configuration, the amount of light leaking from the
lens through the first region 161 (that is, the amount of light
passing through the first region 161) can be reduced, and therefore
the light that has returned to the light entrance surface 11 side
can be utilized effectively.
Next, with reference to FIGS. 3 to 8, how the light emitted from
the light source 20 travels will be described in more detail by
taking the light emitted from the starting point Q as a typical
example.
FIG. 3 shows optical paths of light rays that enter the lens
through the light entrance surface 11 and reach the first light
exit surface 121. The light ray that has reached the transmissive
region 123 due to a small angle with respect to the optical axis A
(see FIG. 2) is refracted at the first light exit surface 121 and
then reaches the surface to be irradiated 3. The light rays that
have reached the total reflection region 124 due to larger angles
with respect to the optical axis A (see FIG. 2) are totally
reflected at the first light exit surface 121 and then travel
inside the main body 1A.
FIG. 4 shows optical paths of light rays that enter the lens
through the light entrance surface 11 and reach the second light
exit surface 122. The light rays that have reached the second light
exit surface 122 are refracted at the second light exit surface 122
and then reach the surface to be irradiated 3.
FIG. 5 shows optical paths of light rays that are totally reflected
at the total reflection region 124 of the first light exit surface
121 as described in FIG. 3 and reach the second light exit surface
122. The light rays that have reached the second light exit surface
122 are totally reflected one or more times at the second light
exit surface 122 so that they travel along the second light exit
surface 122 in the main body 1A and enters the ring portion 1B.
Although not illustrated here, some of the light rays are not
totally reflected at the second light exit surface 122 and exit the
main body 1A.
FIG. 6 shows optical paths of light rays that enter the ring
portion 1B as described in FIG. 5 and reach the first region 161 of
the back surface 16 of the ring portion 1B. The light rays that
have reached the first region 161 are totally reflected one or more
times at the first region 161 so that they travel toward the second
region 162 or the end surface 17. Although not illustrated here,
some of the light rays are not totally reflected at the first
region 161 and exit the ring portion 1B.
FIG. 7 shows an optical path of a light ray that is totally
reflected at the first region 161 as described in FIG. 6 and
reaches the second region 162 of the back surface 16 of the ring
portion 1B. The light rays that have reached the second region 162
are totally reflected at the second region 162 one time and travel
toward the end surface 17. Although not illustrated here, some of
the light rays are not totally reflected at the second region 162
and exit the ring portion 1B.
FIG. 8 shows optical paths of light rays that are totally reflected
at the first region 161 and the second region 162 of the back
surface 16 as described in FIG. 6 and FIG. 7 and reach the end
surface 17. The light rays that have reached the end surface 17 are
refracted at the end surface 17 and reach the surface to be
irradiated 3.
In the illuminating lens 1 configured as described above, the most
part of the light that has been emitted from the light source 20
and reached the transmissive region 123 located in the center of
the first light exit surface 121 is refracted at the transmissive
region 123, and thus the area surrounding the optical axis A of the
lens on the surface to be irradiated 3 is irradiated with the
refracted light. On the other hand, the most part of the light that
has been emitted from the light source 20 and reached the total
reflection region 124 located on the peripheral side of the first
light exit surface 121 is totally reflected at the total reflection
region 124. The most part of the totally reflected light enters the
ring portion 1B and exits the ring portion 1B through the end
surface 17, and then the surface to be irradiated 3 is irradiated
with that light. Furthermore, the most part of the light that has
been emitted from the light source 20 and reached the second light
exit surface 122 is refracted at the second light exit surface 122,
and thus the area away from the optical axis A of the lens on the
surface to be irradiated 3 is irradiated with the refracted light.
Accordingly, the illuminating lens 1 of the present embodiment
allows the range of transmission directions for light from the
light source 20 to be widened further.
Furthermore, in the present embodiment, the light that has returned
to the light entrance surface 11 side also can be guided in the
direction away from the optical axis by the ring portion 1B. As a
result, a wider illuminance distribution on the surface to be
irradiated 3 can be obtained. In addition, such control of the
light that has returned to the light entrance surface 11 side makes
it possible to prevent the illuminance distribution on the surface
to be irradiated 3 from being influenced by the configuration and
reflectance of a structural member disposed behind the illuminating
lens 1.
The illuminating lens of the present invention also is applicable
to light sources (such as lasers and organic ELs) as well as light
emitting diodes.
In the present embodiment, the light exit surface 12 is
axisymmetric with respect to the optical axis A (circular shape in
plan view). The light exit surface 12, however, need not be
axisymmetric with respect to the optical axis A. For example, as
shown in FIG. 20A, the light exit surface 12 may have an elliptical
shape when viewed from the optical axis direction. In this case,
the ring portion 1B also has an elliptical shape similar to that of
the light exit surface 12 in plan view. This illuminating lens 1 is
suitable particularly for an elongated light source. Alternatively,
as shown in FIG. 20B, the light exit surface 12 may have a rounded
rectangular shape when viewed from the optical axis direction.
Second Embodiment
FIG. 9 is a schematic diagram of a lighting device 7 according to a
second embodiment of the present invention. This lighting device 7
includes a light emitting diode 2 for emitting light, and an
illuminating lens 1 of the first embodiment for spreading light
emitted from the light emitting diode 2 so that the surface to be
irradiated 3 is irradiated with the spread light.
The light emitting diode 2 is in contact with the light entrance
surface 11 of the illuminating lens 1 via a bonding agent, and
connected optically to the light entrance surface 11. The light
that has exited the illuminating lens 1 through the light exit
surface 12 reaches the surface to be irradiated 3, and thus the
surface to be irradiated 3 is illuminated with that light.
Light generation in the light emitting diode 2 has no directivity
in itself, and a light emitting region has a refractive index of at
least 2.0. When light from the light emitting region enters a low
refractive region, the refraction of the light at the interface
causes the light to have the maximum intensity in the normal
direction of the interface and to have a lower intensity as the
angle of the light with respect to the normal line increases. As
described above, since the light emitting diode 2 has high
directivity, it is necessary to widen the range of transmission
directions for light therefrom using the illuminating lens 1 to
illuminate a larger area.
FIG. 10 is a graph showing the effects of the illuminating lens 1.
A dotted line in FIG. 10 shows the illuminance distribution on the
surface to be irradiated 3 obtained by using the lighting device 7
of the second embodiment. A solid line in FIG. 10 shows the
illuminance distribution on the surface to be irradiated 3 obtained
when a reflecting plate 60 is disposed behind the lighting device 7
of the second embodiment as shown in FIG. 11. A difference between
the solid line and the dotted line in FIG. 10 indicates the
influence of the reflecting plate 60.
FIG. 12 is a graph showing the influence of the reflecting plate 60
for the illuminating lens 110 that has been conceived before. A
dotted line in FIG. 12 shows the illuminance distribution on the
surface to be irradiated 3 obtained by using a lighting device
including the illuminating lens 110 that has been conceived before
(i.e., a lens corresponding to the illuminating lens 1 without the
ring portion 1B) and the light emitting diode 2, as shown in FIG.
13. A solid line in FIG. 12 shows the illuminance distribution on
the surface to be irradiated 3 obtained when the reflecting plate
60 is disposed behind the lighting device of FIG. 13, as shown in
FIG. 14. A difference between the solid line and the dotted line in
FIG. 12 indicates the influence of the reflecting plate 60.
A comparison between FIG. 10 and FIG. 12 shows that when the
lighting device 7 of the second embodiment is used, the illuminance
distribution on the surface to be irradiated 3 is less influenced
by a structural member disposed behind the illuminating lens 1.
As an example of specific numerical values of the present
invention, Example 1 is shown below.
Example 1
FIG. 15 is a schematic diagram of an illuminating lens used in
Example 1 of the lighting device according to the second embodiment
of the present invention. Example 1 is a design example designed to
widen the range of transmission directions for light from a 0.5 mm
cubic-shaped light emitting diode as a light source.
As shown in FIG. 15, in Example 1, the radius of the light entrance
surface 11 of the main body 1A is 2.4 mm, and the width of the
second region 162 of the back surface 16 of the ring portion 1B is
4.0 mm. In a cross-sectional view including the optical axis A, the
first region 161 of the back surface 16 has a shape of a circular
arc with a radius of 1.6 mm, and the center of the circle is
located 4.0 mm away from the optical axis A on the front surface 18
of the ring portion 1B.
Next, Table 1 below shows specific numerical values of the light
exit surface 12 of the main body 1A.
TABLE-US-00001 TABLE 1 .theta.i (deg) sagY (mm) 0.000 0.800 0.715
0.801 1.425 0.804 2.126 0.808 2.814 0.814 3.489 0.820 4.149 0.827
4.794 0.835 5.425 0.842 6.041 0.850 6.643 0.859 7.231 0.867 7.805
0.875 8.366 0.884 8.914 0.893 9.450 0.901 9.973 0.910 10.485 0.919
10.985 0.927 11.474 0.936 11.952 0.945 12.420 0.954 12.878 0.962
13.326 0.971 13.764 0.980 14.194 0.988 14.615 0.997 15.027 1.006
15.431 1.014 15.828 1.023 16.216 1.032 16.598 1.040 16.973 1.048
17.340 1.057 17.702 1.065 18.057 1.074 18.406 1.082 18.750 1.090
19.088 1.098 19.421 1.106 19.748 1.114 20.072 1.122 20.390 1.130
20.704 1.138 21.014 1.145 21.320 1.153 21.623 1.160 21.921 1.168
22.217 1.175 22.509 1.182 22.798 1.190 23.084 1.197 23.368 1.203
23.649 1.210 23.928 1.217 24.204 1.224 24.479 1.230 24.751 1.236
25.022 1.243 25.291 1.249 25.559 1.255 25.825 1.260 26.090 1.266
26.354 1.272 26.616 1.277 26.878 1.282 27.139 1.288 27.400 1.293
27.660 1.297 27.919 1.302 28.178 1.307 28.436 1.311 28.695 1.315
28.953 1.319 29.212 1.323 29.470 1.327 29.728 1.331 29.987 1.334
30.246 1.338 30.506 1.341 31.025 1.347 31.286 1.349 31.547 1.352
31.809 1.354 32.072 1.357 32.335 1.359 32.599 1.360 32.863 1.362
33.128 1.364 33.394 1.365 33.661 1.367 33.928 1.368 34.196 1.369
34.465 1.370 34.734 1.370 35.003 1.371 35.273 1.371 35.543 1.372
35.813 1.372 36.084 1.372 36.354 1.372 36.624 1.372 36.894 1.372
37.162 1.372 37.430 1.372 37.696 1.372 37.961 1.371 38.224 1.371
38.485 1.371 38.743 1.371 38.998 1.371 39.249 1.371 39.495 1.371
39.746 1.371 40.007 1.370 40.266 1.369 40.525 1.369 40.782 1.368
41.038 1.367 41.293 1.366 41.546 1.365 41.799 1.365 42.050 1.364
42.300 1.363 42.550 1.362 42.798 1.361 43.045 1.360 43.290 1.359
43.535 1.358 43.799 1.357 44.022 1.355 44.264 1.354 44.505 1.353
44.745 1.352 44.985 1.351 45.223 1.349 45.461 1.348 45.697 1.347
45.933 1.345 46.168 1.344 46.403 1.343 46.636 1.341 46.869 1.340
47.101 1.338 47.333 1.336 47.564 1.335 47.794 1.333 48.024 1.331
48.253 1.330 48.481 1.328 48.709 1.326 48.937 1.324 49.164 1.322
49.391 1.320 49.617 1.318 49.843 1.316 50.068 1.314 50.293 1.312
50.518 1.310 50.742 1.308 50.966 1.305 51.190 1.303 51.414 1.301
51.637 1.298 51.861 1.296 52.084 1.293 52.307 1.290 52.530 1.288
52.753 1.285 52.976 1.282 53.199 1.279 53.421 1.276 53.644 1.273
53.867 1.270 54.090 1.267 54.314 1.264 54.537 1.261 54.761 1.257
54.984 1.254 55.208 1.251 55.433 1.247 55.658 1.243 55.883 1.240
56.108 1.236 56.334 1.232 56.560 1.228 56.787 1.224 57.014 1.220
57.242 1.216 57.470 1.212 57.699 1.208 57.929 1.203 58.159 1.199
58.390 1.194 58.622 1.189 58.854 1.184 59.087 1.180 59.322 1.175
59.557 1.170 59.793 1.164 60.030 1.159 60.268 1.154 60.507 1.148
60.747 1.143 60.989 1.137 61.231 1.131 61.475 1.125 61.720 1.119
61.967 1.113 62.215 1.107 62.464 1.100 62.715 1.094 62.967 1.087
63.221 1.080 63.477 1.073 63.734 1.066 63.993 1.059 64.254 1.051
64.516 1.044 64.781 1.036 65.047 1.028 65.316 1.020 65.587 1.012
65.856 1.004 66.135 0.995 66.412 0.987 66.692 0.978 66.974 0.969
67.259 0.960 67.546 0.951 67.836 0.941 68.129 0.931 68.424 0.921
68.723 0.911 69.024 0.901 69.329 0.890 69.637 0.880 69.948 0.869
70.263 0.858 70.581 0.846 70.902 0.834 71.228 0.823 71.557
0.810
In Table 1, .theta.i is an angle between the optical axis A and a
straight line connecting the position of the light source (starting
point Q) on the optical axis A and an arbitrary point on the light
exit surface 12. Furthermore, in Table 1, sagY is a distance along
the optical axis A between the light source position (starting
point Q) on the optical axis A and the arbitrary point on the light
exit surface 12. FIG. 16 is a graph obtained by plotting the values
of .theta.i and sagY in Table 1.
Third Embodiment
FIG. 17 is a schematic diagram of a surface light source 9
according to a third embodiment of the present invention. This
surface light source 9 includes a plurality of lighting devices 7
of the second embodiment arranged in a plane, and a diffusing plate
4 disposed to cover the plurality of lighting devices 7. The
lighting devices 7 may be arranged in a matrix as shown in FIG. 17.
They may be arranged in a staggered manner. In FIG. 17, the ring
portion 1B of the illuminating lens 1 is not illustrated for
simplification of the drawing.
The surface light source 9 includes a substrate 8 facing the
diffusing plate 4 with the lighting devices 7 being disposed
therebetween. As shown in FIG. 18, the light emitting diode 2 of
each lighting device 7 is mounted on the substrate 8 via an
interposer substrate 81. In the present embodiment, a reflecting
plate 6 is disposed on the substrate 8 to cover the substrate 8
with the light emitting diodes 2 being exposed.
The lighting device 7 emits light to one surface 4a of the
diffusing plate 4. That is, the one surface 4a of the diffusing
plate 4 is the surface to be irradiated 3 that has been described
in the first and second embodiments. The diffusing plate 4 emits
the light received on its one surface 4a from the other surface 4b
in a diffused manner. The lighting devices 7 emit light
individually toward a large area of the one surface 4a of the
diffusing plate 4 so that the one surface 4a has a uniform
illuminance, and upon receiving this light, the diffusing plate 4
emits the light diffusely. As a result, the surface light source
capable of emitting light having less uneven brightness in the
plane is obtained.
The light emitted from the lighting device 7 is diffused by the
diffusing plate 4 so that the diffuse light returns to the lighting
device side or passes through the diffusing plate 4. The light that
has returned to the lighting device side and struck the reflecting
plate 6 is reflected at the reflecting plate 6 and again enters the
diffusing plate 4.
Fourth Embodiment
FIG. 19 is a schematic diagram of a liquid-crystal display
apparatus according to a fourth embodiment of the present
invention. This liquid-crystal display apparatus includes a
liquid-crystal panel 5, and a surface light source 9 of the third
embodiment disposed behind the liquid-crystal panel 5.
A plurality of lighting devices 7 each including the light emitting
diode 2 and the illuminating lens 1 are arranged in a plane, and
the diffusing plate 4 is illuminated by these lighting devices 7.
The underside (one surface) of the diffusing plate 4 is irradiated
with the light emitted from the lighting devices 7 to have a
uniform illuminance, and then the light is diffused by the
diffusing plate 4. Thus, the liquid-crystal panel 5 is illuminated
by the diffused light.
It is preferable that an optical sheet such as a diffusing sheet or
a prism sheet is disposed between the liquid-crystal panel 5 and
the surface light source 9. In this case, the light that has passed
through the diffusing plate 4 further is diffused by the optical
sheet and illuminates the liquid-crystal panel 5.
The invention may be embodied in other forms without departing from
the spirit or essential characteristics thereof. The embodiments
disclosed in this specification are to be considered in all
respects as illustrative and not limiting. The scope of the
invention is indicated by the appended claims rather than by the
foregoing description, and all changes which come within the
meaning and range of equivalency of the claims are intended to be
embraced therein.
* * * * *